Activated macrophages can participate in the immune response by nonspecifically engulfing and killing foreign pathogens within the macrophage, by displaying degraded peptides from foreign proteins on the macrophage cell surface where they can be recognized by other immune cells, and by secreting cytokines and other factors that modulate the function of T and B lymphocytes, resulting in further stimulation of immune responses. Activated macrophages can also contribute to the pathophysiology of disease in some instances. For example, activated macrophages can contribute to atherosclerosis, rheumatoid arthritis, autoimmune disease states, and graft versus host disease.
Atherosclerosis is initiated when a fatty streak forms within a blood vessel wall. Formation of fatty streaks is believed to result from accumulation of lipoprotein particles in the intima layer of the blood vessel wall, the layer of the vessel wall underlying the luminal endothelial cell layer. Lipoprotein particles can associate with extracellular matrix components in the intima layer and can become inaccessible to plasma antioxidants, resulting in oxidative modification of the lipoprotein particles. Such oxidative modification may trigger a local inflammatory response resulting in adhesion of activated macrophages and T lymphocytes to the luminal endothelium followed by migration into the intima layer. The oxidized lipoprotein particles themselves can act as chemoattractants for cells of the immune system, such as macrophages and T cells, or can induce cells in the vascular wall to produce chemoattractants. The atherosclerotic lesion then forms a fibrous cap with a lipid-rich core filled with activated macrophages. Atherosclerotic lesions that are unstable are characterized by local inflammation, and lesions that have ruptured and have caused fatal myocardial infarction are characterized by an infiltration of activated macrophages and T lymphocytes.
The present invention relates to a method of identifying/monitoring active atherosclerotic plaques in blood vessel walls. In accordance with the invention a ligand, that binds to a receptor which is preferentially expressed/presented on the surface of activated macrophages relative to resting macrophages, is conjugated to a chromophore or a chemical moiety capable of emitting radiation and the ligand conjugates are administered to a patient being evaluated for atherosclerosis. The ligand conjugates bind to activated macrophages associated with active atherosclerotic plaques and emit light (i.e., ligand-chromophore conjugates) or radiation (i.e., ligand-chemical moiety conjugates) and can be detected using a catheter-based device or by external imaging, such as by using X-ray detection. Accordingly, the ligand conjugates can be used to distinguish active atherosclerotic plaques containing activated macrophages from inactive plaques.
Methods are not presently available for distinguishing active and inactive atherosclerotic plaques. Because many unstable (i.e., active) atherosclerotic plaques, capable of rupturing and causing acute atherosclerotic syndromes do not produce luminal narrowing of blood vessels, particularly in the coronary circulation, the method of the present invention represents a significant advance in diagnosing the risk of myocardial infarction, and in evaluating the need for clinical intervention, in patients suffering from atherosclerosis.
In one embodiment, a method is provided of identifying/monitoring active atherosclerotic plaques associated with blood vessel walls wherein the plaques comprise activated macrophages having accessible binding sites for a ligand. The method comprises the steps of administering to a patient being evaluated for atherosclerosis an effective amount of a composition comprising a conjugate of the general formulaL-Xwherein the group L comprises the ligand and the group X comprises a chromophore capable of emitting light under predetermined conditions, allowing sufficient time for the ligand conjugate to bind to activated macrophages associated with the active plaques, subjecting the blood vessel walls to the predetermined conditions using a catheter-based device, and identifying active plaques by detecting light emitted by the chromophore using a catheter-based device.
In another embodiment, a method is provided of identifying/monitoring active atherosclerotic plaques associated with blood vessel walls where the plaques comprise activated macrophages having accessible binding sites for a ligand. The method comprises the steps of administering to a patient suffering from atherosclerosis an effective amount of a composition comprising a conjugate of the general formulaL-Xwherein the group L comprises the ligand and the group X comprises a chemical moiety capable of emitting radiation, allowing sufficient time for the ligand conjugate to bind to the activated macrophages associated with the active plaques, and identifying active plaques by detecting radiation emitted by the chemical moiety using a catheter-based device or by external imaging, such as by X-ray detection.
In these embodiments, the ligand can be any ligand that binds to a receptor which is preferentially expressed/presented on the surface of activated macrophages relative to resting macrophages. Such ligands include vitamins selected from the group consisting of folate, biotin, vitamin B12, riboflavin, thiamine, and other vitamin receptor binding ligands.